A tire-pressure control apparatus of such a type is disclosed in, for example, Japanese Patent Application Laid-Open (kokai) No. H7-137515.
In the tire-pressure control apparatus disclosed in the above-mentioned publication, a pressure sensor capable of detecting tire pressure is disposed in an air passageway extending between a tire air chamber and a control valve device, and operation of the control valve device is electrically controlled on the basis of the pressure detected by means of the pressure sensor. The tire-pressure control apparatus can operate an air pump and bring the control valve device into an open state (a state in which compressed air is supplied from the air pump to the air passageway in which the pressure sensor is disposed) with a manual cock disposed between the pressure sensor and the tire air chamber closed; sense a change in the air pressure within the air passageway at the time by use of the pressure sensor; and determine that an anomaly, such as leakage of air, has occurred in the air passageway when the rate of air pressure increase is slower than a predetermined rate.
However, the determination as to whether or not an anomaly, such as leakage of air, has occurred is performed under the assumption that the air pump operates normally. Therefore, if the air pump does not operation normally (for example, the air discharging function of the air pump has deteriorated), such a state (the discharge anomaly of the air pump) cannot be detected. In such case, despite occurrence of an air leakage anomaly, the rate of air pressure increase becomes slower than the predetermined rate, leading to an erroneous determination.